Marking quartz



Filed March 2, 1926 Inventor" I Sylvester Boyer",

His Attorney Patented June 7, 1932 UNITED STATES PATENT OFFICE SYLVESTER BOYER, 'OIE LYNN, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK MARKING- QUARTZ Application filed March 2, 1926, Serial No. 91,843.

My present invention relates to means for marking quartz and more particularly to means for marking quartz which may be sub- 1 jected to relatively high temperatures, such as quartz thermometers of the type disclosed in my copending application, Serial No. 70,191, filed November 19, 1925.

The marking of athermometer or glass vessel of any type usually comprises two steps, first the etching of a mark on the glass, and second the placing of a contrasting material on the etched mark whereby the position or character of the mark may be made clearly visible. The marking of quartz, however, involves certain difliculties- For example, it has hitherto been impossible to etch fused quartz so as to produce a clearly defined line or design thereon. Attempts'to etch quartz by well known methods, as .by coating the quartz with paraflin and producing a mark through the paraflin on the quartz and then placing the coated quartz in cold or unheated.

hydrofluoric acid, have resulted uniformly in failure due to the fact that the etching pro duced in such cases extends, as a rule, over the entire surface of the quartz, and isnot confined to the marked places. Further difficulty. is encountered in marking quartz which is subjected to relatively high temperatures, as in the case of quartz thermometers, since it is necessary that such marks should be colored inorder to be clearly visible, and should furthermore be capable of withstanding the high temperatures encountered in the use of such thermometers without causing discoloration of the uartz body.

It is one of the ob ectsof m invention to provide a marking on quartz hich shall be sharply defined,.clearly visible, stable, and permanent in character even when exposed to temperatures in the neighborhood of 1000 C.

The acompanying drawing shows in ele vation a quartz thermometer embodying the features of my invention.

The uartz thermometer 1 may be provided wlth a central-bore 2 having a bulb3 adapted to contain a quantity of gallium or other suitable material. I preferably employ in connection with the thermometer an expansion chamber as indicated at 4, for purfilling of the thermometer with the expansible'" material.

To produce a sharply defined etched mark on the quartz, hydrofluoric acid, preferably dilute, and heated to a temperature of approximately 80 (1., may be conveniently employed. Since the paraffin co'ating usually employed in etching glass would melt far below such a temperature, it is necessary to employ a protective coating for the quartz which will remain on the quartz body at least for the duration of the etching period.

In the process employed, the quartz is first cleaned in any suitable manner and then heated either in a free flame or oven to a dull redness. The quartz is then immersed in a polymerizable or oxidizable material, such as chinawood or linseed oil, or, if desired, a japan varnish, and allowed to remain therein for a relatively short period of time, for example,'one or two minutes, or until any possible film of air on the quartz surface has been completely replaced by the oil. The quartz is now removed frpm the oil and held above a free flame or heated in an oven until a distinct colorationoccurs indicatin that polymerization has taken place. The egree of polymerization will vary with thetype of marking desired on the quartz. If a very fine mark is desired, the oil is polymerized to the extent of becoming quite hard, while if a rather wide mark is desired the polymerizationv should not be carried so far. Marks are now made through the oil coating and on to the quartz surface, the marks penetratminutes, depending on the nature of the mark desired. If a mark having sharp edges as desired, a period of from 8 to 10 minutes wlll prove satisfactory, while if a mark havin a rounded edge is desired, the quartz should be exposed to the acid for a longer period of time. After the quartz has been acted upon by the acid for a suitable time, it is taken out of the acid and the oil coating removed. This may be easily accom lished as the oil coating usually tends to ecome loosened from the quartz surface during the latter portion of the etching operation.

In order to make the etched mark on the quartz clearly visible, it is necessary to place on the etching some colored materlal. If the quartz is to be employed in the measurement of high temperatures, it is also essential that the coloring matter be stable under high temperature conditions. I have found that a very desirable grayish black mark may be produced by a quantity of copper oxide and fine sand or silica suspended in glycerine. About six parts of the oxide and one part silica when added to sufficient glycerine to produce a material which may be used as an ink, gives a very satisfactory mixture. The liquid may be placed on the etched portion of the quartz with an ordinary pen or in any other suitable manner, although it will be found that a specially prepared pen which Will more or less confine the liquid to the etched portions will give the best results. The marked portion of the quartz is now held above a free flame and heated slightly to evaporate the glycerine. Evaporation should be carried out slowly in order to confine the colored material within the etched mark. After the glycerine is driven off the quartz is heated in the oxidizing portion of a free flame to redness, or until fusion of the oxide, silica, and quartz is complete.

Quartz marked in the manner described above has been subjected to temperatures as high as 1100 C. for relatively long periods of time without causing deterioration of the markings or any discoloration of the quartz body. I have, furthermore, found such a marking to be insoluble in the ordinary laboratory reagents, such as hot and cold sodium hydroxide, hot and cold nitric acid, hydrochloric acid and aqua regia.

If desired another colored mark may be obtained by the use of a mixture comprising five parts lead oxide (litharge), one part silica, and about parts cobalt oxide, suspended in glycerine and placed on the etched portion of the quartz and heated as above described. The proportions of the oxides given may vary considerably without showing marked changes in the final result. If desired, a green marking may be obtained by taking a mixture comprising three parts lead oxide, one part silica and about 28 parts barium ehromate, suspended in glycerine,

placing the liquid mixture on the etched mark and heating in the manner previously set forth.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A thermometer formed from fused quartz and having vitreous contrasting markings fused thereon, said markings being composed of material which is stable at a temperature up to and in excess of 500 C.

2. A thermometer formed from fused quartz and provided with markings on the surface thereof, said markings being composed of colored vitreous silica fused on said surface and being stable up to and at a temperature of approximately 1,000 C.

3. An article of manufacture formed from fused quartz and provided with markings on the surface thereof, said markings being composed of colored vitreous silica fused on said surface and being stable up to and at a temperature of approximately 1,000 C.

In Witness whereof, I have hereunto set my hand this 26th day of February, 1926.

SYLVESTER BOYER. 

